1. Field
This application relates to the field of reliable and efficient data networking, and more particularly to the field of variable-strength error correction and resource allocation in a noisy data networking environment.
2. Description of Related Art
Throughput of a digital data communication channel may be adversely affected by an excessive Bit Error Rate (BER) due either to the inherent characteristics of the channel or to interference caused by other users of the channel. Error correction coding schemes may improve the reliability of data transmissions by reducing the delivered bit error rate. Error correction coding allows for correction of received data. Correcting the data in this manner reduces the amount of re-transmissions, which is generally inefficient in that it includes both a request for re-transmission from the data recipient and a re-transmission by the original sender of the data. Such re-transmissions use physical bandwidth of the channels that would otherwise be available data communication.
Using error correction coding adds data overhead and thus also reduces the amount of physical bandwidth available for data transmission. Accordingly, the choice of an error correction code involves balancing expected gains of improved channel accuracy (with a corresponding reduction in re-transmitted data) against the overhead introduced by the error correction code. Note that a particular code's resilience to errors (i.e., the number of errors which can be corrected per a given number of bits transmitted, also sometimes referred to as a code's “strength”) is proportional to the overhead introduced by the code. Generally, a strong code will introduce more overhead than a weak code. Thus, using a code that is too weak could cause too many re-transmissions due to too many errors in the received data while using a code that is too strong could increase overhead unacceptably.
In over-the-air transmission of TCP/IP packets, it is sometimes difficult to use an acceptable code strength due to the criticality of receiving the TCP/IP header intact. The header contains important information about the packet, including the size of the data being transmitted (i.e., the payload), the packet number (used to identify and sequence the packets) the data source, and the data destination. If a packet header is damaged, it may be difficult to request a retransmission since critical packet information may be lost. Thus, in some instances, using an error correction code that is strong enough to provide an acceptable delivered BER for the packet header may increase the overhead unacceptably when applied to the entire packet. However, using a code that is too weak could result in too many requests for retransmission, since receipt of the packet header without any errors is important.
Furthermore, in a network of digital radios, a channel is often shared by multiple terminals. Some of the applications that are being run over these terminals have quality of service requirements. For example, IP voice requires a minimum bandwidth, e.g., 16 kilobits per second, to be clearly understood by the end user. An effective way to share a common channel among multiple terminals, and still fulfill quality of service requirements, is to make use of packet scheduling algorithms. These algorithms rank IP packets per their quality of service requirements, and schedules their transmission time accordingly. However, use of error correcting codes reduces the available physical bandwidth due to the associated overhead. In an environment where a channel is shared by multiple terminals, several applications with diverse quality of service requirements may have to be supported. Since these applications will require different levels of coding, some applications may consume more bandwidth than others. If the packets scheduling algorithm does not take into account differences in consumed bandwidth, it may unfairly favor one user over another, or, it may fail to provide the intended bandwidth to some of the users.